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02-28-2012, 07:53 AM   #31
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QuoteOriginally posted by GibbyTheMole Quote
After reading this thread yesterday, I decided to test all of my lenses to see what kind of difference the UV filter had on IQ.
Did you use lens hoods for all of your lenses? In bright conditions, the contrast degradation by not using a hood is quite high and it can mask other aspects of image quality.

02-28-2012, 12:32 PM   #32
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QuoteOriginally posted by demp10 Quote
Did you use lens hoods for all of your lenses?
Yep. Except for the 50mm.
02-28-2012, 05:34 PM   #33
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QuoteOriginally posted by KevinR Quote
I've tended to be a UV filter addict from the old school of protect the lens thought. But was playing with my Sigma 170-500 on the new K-5 a bit over a month ago, and while doodling thought of comparing images with and without the UV filter.

I tried to keep things the same as best possible, although focus points might not be perfectly the same, and the results seem to show an appreciate IQ degradation with the filter on. I did a few repeats on roof tiles and paving bricks with similar results, but the image of the aerial bracket seems to show best what looks to me like a fine-fine mist over all the images with the filter on. The sand grain detail on tiles and cracks on black insulation of the solar heater on the second series are also distictive. This was shot something like anti-clockwise starting top left.

Anyone else done tests with positive degrading results? Filter was Kenko UV Japan

Should I be thinking of binning or selling off these UV front element protectors.

Typically around 500mm 1/500s f/13 iso200

FWIW, I've found with all my long lenses that any filter seems to degrade their quality. When I bought my A*600/5.6 it had a big Tamron filter on the front which I decided to leave on, given the dollar value and rarity of the lens. After spending some frustration because I couldn't get a sharp picture from the thing, I removed the filter, which cured the degradation.
That filter is now sitting under a small statue of my Rottweiler in my wife's ornament cabinet.
It works very well for this purpose, as a lens accessory, not so much.
02-28-2012, 07:07 PM   #34
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QuoteOriginally posted by Anvh Quote
...
I'm not against using filters but i don't believe a filter will protect the lens if you bump into somthing or if a stone gets throw to it.
The filter is very thing glass so it will shatter and those sharp shatters will probably scratch the coating..
this statement seems reasonable enough, but i recently bought several filters of various brands & sizes to remove the glass and use the rings as spacers and was shocked at how many hits with a hammer and centerpunch i had to make before they cracked. I am definitely convinced they offer structural protection to a fragile front element.
Moreover, last weekend while on a photo hike, my buddy's tripod mounted camera(Nikon D300) did a faceplant and smacked hard on the street, filter first. The filter was smashed and the threads were bent but the front element had not a scratch. we blew away the glass shards and he took a few pics which were perfectly sharp. Had there been no filter, that lens would have been a goner. it is quite pointless to argue the utility of protective filters because they certainly have value for certain situations and are undesirable other times. let's get over it and move on.

02-29-2012, 11:15 AM   #35
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QuoteOriginally posted by GibbyTheMole Quote
.... I chose a shingled roof of a low shed, and a sign with white lettering as the subject of the test. The shingles for contrast & detail, and the sign for CA. All shots were taken at f8/ISO200 on a sunny day. I focused carefully, took the shot with the filter, removed the filter, refocused and took the same shot from the same spot. In the case of my zooms, I shot at the widest focal length, in the middle of the range, then at the long end to check the entire range. Lens hood was used in all cases & the camera was a K-x.

I was surprised to find very little difference (if any) in the majority of the shots when viewed at full resolution at the point of focus. There were a couple of exceptions: The Tair 500mm mirror lens was decidedly better without the UV filter, and most surprisingly, the Tamron 60-300 (model 23a) was actually a little better with the filter. (I know! I was blown away by that result as well. I may repeat that test, since that makes no sense, unless the filter is actually doing it's job in the UV department, which is doubtful.)

I fully expected definite IQ degradation with the filters present. What makes it even more of a shock, is the filters are with one exception, cheap Massa, Zeikos, & Prinz filters.

Weird, huh?
No, I don't find that weird at all. Filter IQ degradation will only be really visible, if you use a very good lens, to start with. Mediocre filters on a so, so lens, won't add much in terms of contrast and sharpness loss. That the Tammy might in fact benefit from the UV filter can have several reasons, but cutting away UV is certainly helpful. It is the same with the Tammy 300/2.8, which benefits visibly from using the UV filters. (one in front and one in the rear.)

I would also like to point out one problem with your test: a sunny day! Roofs are usually much warmer on a sunny day (the shingles, you mentioned), than the surrounding air and thus will create air turbulence, which limits the resolution you can achieve with even the best lens. Astronomers or nature photographers who use long lenses, do know that "seeing" effect quite well.

Ben
02-29-2012, 11:52 AM   #36
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QuoteOriginally posted by Ben_Edict Quote
Filter IQ degradation will only be really visible, if you use a very good lens, to start with. Mediocre filters on a so, so lens, won't add much in terms of contrast and sharpness loss
I wouldn't call the M50 1.4 "mediocre". Or the Pentax 35-105. Or the Tamron 60-300.
02-29-2012, 12:49 PM   #37
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QuoteOriginally posted by GibbyTheMole Quote
I wouldn't call the M50 1.4 "mediocre". Or the Pentax 35-105. Or the Tamron 60-300.
That depends very much on the aperture setting you used. the M 50 is by no means a first rate lens anywhere near its max. aperture, for instance. But, apart from that, I really think, that photographing roof shingles on a sunny day does not validate differences in sharpness, as the local turbulence will vary very much from pic to pic and contribute probably much more to the perceived differences than the filters.

Ben
02-29-2012, 01:23 PM   #38
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All shots were at f8 on all lenses at ISO200.

So, under what conditions would you test? Subject matter, lighting, etc.

03-01-2012, 01:29 AM   #39
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It makes sense that IQ degradation due to UV filters would only be appearant in very good lenses.

To me personally it was easy to see when I used the razorscharp DA 35 ltd. When I took the filter off, I saw microcontrasts and sharpness that I had never seen before.
03-06-2012, 02:36 PM   #40
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QuoteOriginally posted by GibbyTheMole Quote
All shots were at f8 on all lenses at ISO200.

So, under what conditions would you test? Subject matter, lighting, etc.
Try to shoot either indoors, but not under tungsten or emission lighting, unless it is a calibrated standard full spectrum lamp. Or find a place where you can shoot a brick wall, preferably across a lawn (not a paved backyard, which produces turbulence just as heavily as a roof). Also, shoot in the morning, when the air is calm.
IQ degradation will be most obvious with longer lenses, wide angles are unsuitable. Try different apertures, but be aware, that almost all lenses will show increased aberration when fully opened and and fully open aperture will also show more inherent fall-off towards the edges.

Use a short exposure time, as to reduce the influence of air turbulence and try to avoid direct sunshine. Sunshine will produce not only those dreaded turbulences, but will also produce much more contrasty images, which makes it difficult to interpret the final images. Sharpness as such does not exist anyway. What we perceive as "sharpness" is called accutance and is a product of resolution and contrast - thus an increased contrast may affect the image perception in a way which makes it hard to deduce any meaningful results from the pics.

I can understand, that you may find me insisting on avoiding air turbulence quite excessive - I have thought the same in the past. That was until I noticed, that I never ever got a really sharp images from my 500/4.5 taken over a distance (though it is pretty sharp, when taking images of more nearby objects) and then found, that I shared that experience with many other users of long tele lenses. I even disassembled and re-calibrated the lens to no avail, changed the focusing travel etc. Until one day it dawned on me, after following a discussion in another forum, that over longer distances, the images were always ruined by air turbulence.

Ofcourse the effect is more obvious with long glass and long shooting distances - but if you want to scrutinize images for the tiny differences in contrast and resolution, introduced by different filters, you need to reduce all external influences as far as possible. I think I have written a quite long post on testing lenses in the past, but that might have been in another forum as well. But the same basic guidelines apply to filter testing as well.

Ben
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